Ft4 (Free T4)

You should get a Free T4 test if you have symptoms of hypothyroidism, such as fatigue, weight gain, dry skin, or cold intolerance, or of hyperthyroidism, such as weight loss, palpitations, anxiety, or tremors. It is also recommended when TSH is abnormal, during pregnancy, and for monitoring levothyroxine or anti-thyroid treatment.

No special preparation or fasting is required for a Free T4 test. Give your sample in the morning, and take your thyroid medicine after the sample, since levothyroxine can temporarily raise FT4. Stop biotin supplements 48–72 hours before the test, as biotin can interfere with results. Inform your doctor about pregnancy or other medications.

No, fasting is not required for a Free T4 test. You can eat and drink normally before giving your sample. A morning sample is preferred, and you should take your thyroid medicine after the test unless your doctor advises otherwise. Stop biotin supplements 48–72 hours beforehand, as biotin can affect results.